<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .item {
            width: 100px;
            height: 50px;
            border: 1px solid #000;
            float: left;
            margin-right: 10px;
        }
    </style>
</head>

<body>
    <div class="container">
        <h2 class="page-header">点击切换颜色</h2>
        <div class="item"></div>
        <div class="item"></div>
        <div class="item"></div>
    </div>
    <script>
        let items = document.getElementsByClassName('item')

        for (let i = 0; i < items.length; i++) {
            items[i].onclick = function () {
                // this.style.background = 'pink'
                items[i].style.background = 'pink'
            }
        }

    </script>
</body>

</html>